1. Field of the Invention
The present invention generally relates to wireless data communications systems and, more particularly, to link-layer routing for mobile computers.
2. Description of the Prior Art
Many different networking protocols have been defined. For example, the International Business Machines (IBM) Corp. established the System Network Architecture (SNA) which defines a particular protocol permitting communication for IBM and compatible computers. The International Standards Organization (ISO) is an international body that has published standards for Open Systems Interconnection (OSI) architecture. The Defense Data Network (DDN) standard establishes criteria for the Internet Protocol (IP) which supports the interconnection of Local Area Networks (LANs). The IP defines the services provided to users, and specifies the mechanisms needed to support those services. The standard also defines the services required for the lower protocol layer, describes the upper and lower interfaces, and outlines the execution environment services needed for implementation.
The Transmission Control Protocol (TCP) is a transport protocol providing connection oriented, end-to-end reliable data transmission in packet-switched computer LANs and internetworks. The IP and TCP are mandatory for use in all Department of Defence (DoD) packet switching networks which connect or have the potential for utilizing connectivity across network or subnetwork boundaries. Network elements, such as hosts, front-ends, gateways, and the like, within such networks which are to be used for internetworking must implement TCP/IP.
IP is designed to interconnect packet-switched communication LANs to form an internetwork. IP transmits blocks of data, called internet datagrams, from sources to destinations through the internet. Sources and destinations are hosts located on either the same subnetwork or on connected LANs. The DDN standard specifies a host IP. As defined in the DoD architectural model, the IP resides in the internetwork layer. Thus, the IP provides services to transport layer protocols and relies on the services of the lower network protocol. Various network access protocols reside below the IP and may include, for example, an Ethernet protocol, an X.25 protocol, and, of particular interest herein, a wireless medium access protocol.
The Internet protocols were originally developed with an assumption that users, each of which is assigned a unique Internet address, would be connected to the network at fixed locations. However, for portable and handheld computers employing a wireless protocol, the movement or migration or users about the network is typically the rule rather than the exception. As a result, a problem is created in that the implicit design assumptions of the Internet protocol are violated by this type of usage.
Currently, there is no method available which enables mobile computers with wireless data communications equipment to freely roam about while still maintaining connections with each other, unless special assumptions are made about the way the computers are situated with respect to each other. One mobile computer may often be able to exchange data with two other mobile computers which cannot themselves directly exchange data. As a result, computer users in a conference room may be unable to predict which of their associates' computers could be relied upon to maintain network connection, especially as the users moved from place to place within the room.
The problem that arises relates to providing optimal network layer routing with a mobile host when network layer address(es) assigned to that host may not bear any network topological significance. The problem arises because of a requirement for a host to have an identifier that remains fixed, even as the host moves, while at the same time providing sufficient information in the network layer to make network layer routing feasible.